The present invention relates to an antenna and a radio signal detecting device using the same, and more particularly, to an antenna with a wide-band capability, which is fed to a microstrip, and a radio signal detecting device for detecting electromagnetic waves using the same.
Antennas printed on a dielectric substrate have been developed since the late 1970s and used for commercial applications such as global positioning systems (GPS) as well as for military purposes such as airplanes, missiles or rockets. In most applications, tapered slot antennas (TSA) are used. TSAs have many advantages including low profile, light weight, ease of fabrication and installation, high gain, and symmetrical beam patterns. In a TSA, which basically includes a feed, a matching portion, and a radiating portion, a metal surface can be formed in various shapes on a dielectric substrate.
FIGS. 1A and 1B are top and rear views of a TSA. Referring to FIGS. 1A and 1B, a dielectric substrate of the TSA has a metallization surface on both sides thereof. The antipodal TSA, shown in FIGS. 1A and 1B, is formed by gradually flaring strip conductors of a balanced microstrip on opposite sides of the dielectric substrate by an angle a with respect to the antenna axis, thus allowing the antenna to be excited by a microstrip feed.
TSAs have wide-band characteristics and can operate over frequency bands in the range of 10-35 GHz since they exhibit excellent impedance matching and do not include any component depending on a specific frequency. However, while TSAs may be effective in detection or radiation of polarized waves incident parallel to the planes of the TSAs, they suffer from attenuation in excess of about 10 dB of polarized waves incident perpendicularly to the planes. Thus, if vertically polarized waves are to be detected or radiated, the plane of an antenna needs to stand vertically, which is not suitable for apparatuses of small dimensions.
Due to the above problem, it is difficult to apply the TSA to a radio signal detecting device for detecting microwave signals radiated from a speed gun used for measurement of vehicle velocity. Horn antennas are generally used in current radio signal detecting devices.
FIG. 2 is a block diagram showing the configuration of a radio signal detecting device fabricated using a horn antenna. Referring to FIG. 2, if microwave signals radiated from a speed gun are received by a horn antenna 200, the received microwave signals are introduced into a waveguide, and a mixing diode 210 combines the microwave signals with an oscillating signal from a resonator 220 to shift the signals to an intermediate frequency in the waveguide. A demodulator 230 demodulates the signals shifted to the intermediate frequency, and if a controller 240 determines that the demodulated signals are microwave signals radiated from a speed gun, an output unit 250 informs a user of the presence of the speed gun.
However, the radio signal detecting device has problems in that the structure is complicated and it suffers from the loss of a large amount of incident waves since the waveguide having narrow-band-pass characteristics does not propagate a signal whose half-wavelength is smaller than its width.
To solve the above problems, it is a first object of the present invention to provide an antenna having wide band characteristics.
It is a second object of the present invention to provide a radio signal detecting device using the antenna having wide-band characteristics.
In order to achieve the first object, the present invention provides an antenna having wide-band characteristics, which includes: an insulating substrate; a first conductive layer formed on the top surface of the insulating substrate, the first conductive layer having a predetermined width from the front end of the insulating substrate to the rear end thereof; a second conductive layer formed on the bottom surface of the insulating substrate; and first and second conductive plates. The rear end of the first conductive plate is attached to the first conductive layer, the rear end of the second conductive plate is attached to the second conductive layer, and the front ends of the first and second conductive plates are parallel to and separated from each other.
In order to achieve the second object, the present invention provides a radio signal detecting device using the antenna having wide-band characteristics, which includes: an antenna comprising an insulating substrate, a first conductive layer formed on the top surface of the insulating substrate, a second conductive layer formed on the bottom surface thereof, and first and second conductive plates, wherein the rear end of the first conductive plate is attached to the front end of the insulating substrate formed on the top surface thereof, the rear end of the second conductive plate is attached to the bottom surface thereof, and the front ends of the first and second conductive plates are parallel to and separated from each other; a demodulating circuit that demodulates a signal received from the antenna; a central processing unit (CPU) that receives the demodulated signal and determines whether the received signal is a signal radiated from a speed gun, determines the frequency band and intensity of the received signal, and outputs a predetermined signal; and an indicating portion that outputs a visual or auditory signal according to a signal received from the CPU and an output mode selected by a user.